Characterizing the effects of thermal treatment on human norovirus GII.4 viability using propidium monoazide combined with RT-qPCR and quality assessments in mussels

Abstract

This study investigated the effects of thermal treatment (70, 80, and 90 degrees C for 5, 10, and 20 min) on the titers of human norovirus (HuNoV) GII.4, a dominant genotype in fresh mussels using propidium monoazide (PMA) pretreatment and real-time reverse transcription quantitative-polymerase chain reaction (RT-qPCR) and the effects of thermal treatment on mussel quality (Hunter colors and sensory properties). Reductions of > 1-log(10) for HuNoV in PMA-treated mussels required 70 degrees C for 20 min, 80 degrees C for 10 min and 90 C for 5 min. As assessed by PMA/RT-qPCR, the log(10) reduction values of HuNoV in PMA-treated samples was significantly reduced (46% or 0.27 log(10); P < 0.05) when heated to 90 degrees C for 20 min compared with non-PMA treated samples under identical conditions. Hunter color 'L'-, and 'a'- and 'b'- values significantly (P < 0.05) decreased and increased, respectively with a stepwise increase of temperature (70-90 degrees C) and duration of heat treatment (5-20 min). The results of the untrained 7-point hedonic scale of sensory evaluation revealed that mussels heated to 90 degrees C for 10 min were the best quality sample among all thermally treated mussels. The results suggest that the PMA/RT-qPCR method could be very effective in distinguishing HuNoV viability following high heat treatment for an extended duration (eg, 90 degrees C for 20 min). Based on these results, the PMA/RT-qPCR method could be very effective in assessing HuNoV viability following high-heat treatment for an extended duration (eg, 90 C for 20 min). Furthermore, our findings suggest that inactivation of HuNoV GII.4 in the bivalve molluscan shellfish may be accomplished by treatment at 70 degrees C for 20 min, 80 degrees C for 10 min, or 90 degrees C for 5 min. Among all thermal treatments, 90 degrees C for 10 min was considered the optimal cooking temperature and duration for mussels.